1. Field of the Inventions
The inventions disclosed herein are directed to systems, devices and methods for tuning the values of the parameters used in delivering neurostimulation therapy to a patient to provide optimal results from the therapy.
2. Description of the Related Art
Epilepsy, a neurological disorder characterized by the occurrence of seizures (specifically episodic impairment or loss of consciousness, abnormal motor phenomena, psychic or sensory disturbances, or the perturbation of the autonomic nervous system), is debilitating to a great number of people. It is believed that as many as two to four million Americans may suffer from various forms of epilepsy. Research has found that its prevalence can be even greater worldwide, particularly in less economically developed nations, suggesting that the worldwide figure for epilepsy sufferers may be in excess of one hundred million.
Because epilepsy is characterized by seizures, its sufferers are frequently limited in the kinds of activities in which they can participate. Epilepsy can prevent people from driving, working, or otherwise participating in much of what society has to offer. Some epilepsy sufferers have serious seizures so frequently that they are effectively incapacitated.
Furthermore, epilepsy is often progressive and can be associated with degenerative disorders and conditions. Over time, epileptic seizures often become more frequent and more serious, and in particularly severe cases, are likely to lead to deterioration of other brain functions (including cognitive function) as well as physical impairments.
The current state of the art in treating neurological disorders, particularly epilepsy, typically involves drug therapy and/or surgery. The first approach is usually drug therapy. Surgery may include removing portions of the brain or implanting or partially implanting a device that is capable of providing electrical stimulation and/or another type of therapy (e.g., drug therapy).
Electrical stimulation is an emerging therapy for treating epilepsy. However, currently available electrical stimulation devices apply continuous or periodic electrical stimulation to neural tissue surrounding or near implanted electrodes, with out regard to or in response to a particular condition or state that is detected for the patient.
Recent research and clinical studies are directed toward applying electrical stimulation or some other therapy in response or reaction to a detected patient condition, for example, the neurological condition of a patient at the onset of epileptiform activity or just prior to the onset of epileptiform activity indicative of a seizure.
The episodic attacks experienced by a typical epilepsy patient are generally electrographically defined as periods of abnormal neurological activity, sometimes referred to as epileptiform activity. The term “ictal” relates to the physiological condition of a seizure.
Most prior work on the detection and responsive treatment of seizures via electrical stimulation has focused on analysis of electroencephalogram (EEG) and electrocorticogram (ECoG) waveforms. In general, EEG signals represent aggregate neuronal activity potentials detectable via electrodes applied to a patient's scalp. ECoG signals, deep-brain counterparts to EEG signals, are detectable via electrodes implanted on or under the dura mater, and usually within the patient's brain. Unless the context clearly and expressly indicates otherwise, the term “EEG” shall be used generically herein to refer to both EEG and ECoG signals.
Much of the work on detection has focused on the use of time-domain analysis of EEG signals. See, e.g., J. Gotman, Automatic seizure detection: improvements and evaluation, Electroencephalogr. Clin. Neurophysiol. 1990; 76(4): 317-24. In a typical time-domain detection system, EEG signals are received by one or more implanted electrodes and then processed by a control module, which then is capable of performing an action (intervention, warning, recording, etc.) when an abnormal event is detected.
It is generally preferable to be able to detect and treat a seizure at or near its beginning, or even before it begins. The beginning of a seizure is referred to herein as an “onset.” However, it is important to note that there are two general varieties of seizure onsets. A “clinical onset” represents the beginning of a seizure as manifested through observable clinical symptoms, such as involuntary muscle movements or neurophysiological effects such as lack of responsiveness. An “electrographic onset” refers to the beginning of detectable electrographic activity indicative of a seizure. An electrographic onset will frequently occur before the corresponding clinical onset, enabling intervention before the patient suffers symptoms, but that is not always the case. In addition, there are changes in the EEG that occur seconds or even minutes before the electrographic onset that can be identified and used to facilitate intervention before electrographic or clinical onsets occur. This capability would be considered seizure prediction, in contrast to the detection of a seizure or its onset.
U.S. Pat. No. 6,016,449 to Fischell, et al. (which is hereby incorporated by reference as though set forth in full herein), describes an implantable seizure detection and treatment system. In the Fischell system, various detection methods are possible, all of which essentially rely upon the analysis (either in the time domain or the frequency domain) of processed EEG signals. Fischell's controller is preferably implanted intracranially, but other approaches are also possible, including the use of an external controller. When a seizure is detected, the Fischell system applies electrical stimulation, hence Fischell discloses a responsive neurostimulator. The responsive capability is discussed in further detail below.
Currently, however, the process of identifying the optimal stimulation therapy to deliver to a particular patient in response to a neurological event is largely one of trial and error. The clinician or physician typically has a set of different parameters that can be modified and then tested with the patient to see what effect the modifications have on the quality of the treatment. For example, the set of parameters available for the clinician to modify in this device or system “tuning” process may include the amplitude of the stimulation pulse, the pulse width, interval between pulses, the total time over which a given “dose” of stimulation therapy is delivered, which of several electrode combinations are used (e.g., two electrodes, or one electrode referenced to the device case, etc.), and the polarities used, etc. Since these different parameters pose the possibility of many different combinations, when this tuning process is undertaken, it is time consuming and fatiguing, especially for the patient, who is asked to provide feedback with respect to each tested parameter condition. Patient fatigue can result in the patient giving inconsistent feedback (e.g., indicating a positive difference on one occasion when the amplitude is increased, and then indicating no change or a negative effect when the amplitude is increased by the same amount later on.) Moreover, a patient's experience with his or her disease can be different depending on the time of day or other factors, such as hormonal activity. Thus, it can be challenging to reliably tune the stimulation parameters so that they are optimal for a particular patient when the only input to the tuning process is obtained during the patient's sessions with the clinician.